Additive for steel baths

ABSTRACT

A porous, solid-shaped composition for use as a steel-bath additive in the form of blocks containing molybdenum, iron and carbon. The contents and density of the blocks are such that they sink to the slag/metal interface and give an improved dissolution of molybdenum in the bath.

United States Patent Boaden et a1.

1 1 Sept. 23, 1975 ADDITIVE FOR STEEL BATHS Inventors: Kenneth Joseph Boaden, Rectory Rd.. Orsett, Essex; Brian John Edmondson, 51 Berkeley Dr.. Hornchurch, Essex, both of England Filed: June 17, 1974 Appl. No.: 480,155

Foreign Application Priority Data June 15, 1973 United Kingdom.... 28568/73 U.S. Cl. 75/129'; 75/57; 75/176 lnt. Cl. C22C 33/00; C22C 27/04 Field of Search 75/53, 57, 58. 95, 176

References Cited UNITED STATES PATENTS 1/1940 Brennan 75/176 2.881.068 4/1959 Bergh 75/53 3446.614 5/1969 Johnson 3.4911 14 1/1970 Schneider 75/58 Primary Exuminew-P. D. Rosenberg Attorney. Agenl, or Firm-Dennison Dennison. Townshend 8 Meserole 7 13 Claims, No Drawings This invention relates to porous, solid-shaped compositions containing molybdenum, iron and carbon suitable for use as additives forsteel baths.

DESCRIPTION OF THE PRIOR ART Many proposals have been made for the addition of materials to a steel bath so as to improve the properties of the steel. Developments from such proposals have led to the introduction of the additive in an easily handleableform, for example as briquettes. One such proposal is described and claimed inUK patent specification l 215 374which relates to an agglomerate having a molybdenum content of at least 80% by weight. The invention relates to a composition capable of being produced in an easily handleable form and having advantageous properties for introduction and dissolution in the steel bath.

SUMMARY OF THE INVENTION According to the invention there is provided a porous, solid-shaped additive for steel baths which comprises a composition having, by weight, a molybdenum content in the range 40 to 95%, an iron content in the range to 50% and a carbon content in the range 0.2 to 5%, the density of the composition being in the range 2.5to 5.0 grams per cubic centimeter. The preferred molybdenum content is 60 to 70%, the preferred iron content is to 30% and the preferred carbon content is 0.2 to 1.5%. Up to 10% by weight of impurities can generally be tolerated in the composition. The impurities will tend toaccumulate in the slag in the steel bath and will be removed along with it.

A density within the claimed range is found important in order to ensure that the added composition rests at the interface between the molten steel and the molten slag layer. Upon contact with the surface of the molten steel the composition begins to melt and to dissolve into the melt. Preferably the density is within the range 3 to 4 grams'per cubic centimeter.

In order to fall within the desired density range the composition must be held together with a suitable binder. Examples of binders that have been found adequate are molasses, starch,-dextrine and tar.

The presence of iron in the claimed proportions has been found to be advantageous in facilitating dissolution of the molybdenum in the molten steel and represents the improvement of the present composition over previous proposals for agglomerates of high molybdenum content.

The invention also provides a method for making a composition having, by weight, a molybdenum content in the range 40 to 95%, an iron content in the range 10 to 50%, a carbon content in the range 0.2 to 5%, a binder and a density in the range 2.5 to 5 grams per cubic centimeter. which comprises adding together a molybdenum-containing material, an iron-containing material, carbon and a binder and heating the mixture so formed at a temperature in the range 850 to 1500C for a period of at least one hour. The molybdenumcontaining material is preferably molybdenum trioxide. This is the product of roasting molybdenum ore. Pure molybdenum trioxide can be employed if desired and a partly-reduced molybdenum trioxide is also suitable.

Another possible molybdenum-containing starting material is .ammoniu'm molybdate. I

The iron is preferably introduced in the form of iron oxide, conveniently in the form of iron scale. (for example millscale.) but other forms are possible. for ex ample ground iron. The iron-containing material is preferably of a particle size below 30 mesh 885.

The proportion of binder required depends on the particular binder employed but is typically within the range 2 to 5% of the weight of the composition. The binder can if desired be employed in admixture with water. I 1 i The preferred temperature range for forming the composition is 1 150 and 1 350C. Working within this range is found to give a more reduced product, improved strength and less risk of fusion. It also gives a density greater than can be achieved below 1 150C.

Preferably the materials to form the composition are introduced into a cold furnace which is then allowed to warm up to the desired temperature level. This avoids the risk of cracking the compositions that exists in introducing the mixture directly into a hot furnace. The gradual raising of the temperature of the introduced mixture is conveniently achieved by passing the mixture through a tunnel in which the temperature gradually builds up from ambient to the desired working temperature. A particular advantage of the present invention is that the composition lends itself to being formed into a'variety of convenient types. Thus it can be formed into nodules, briquettes and can if desired be extruded into rods. Whichever form is chosen, the discrete lumps of the composition to be added to the steel bath are preferably of a weight in the range 50 to grams.

The products of the invention have the advantage of.

being in a convenient form for introduction to a steel bath and thus avoid the problem of crushing a large block of melted alloy that arises when using ferromolybdenum. The losses of molybdenum that occur in the production of ferromolybdenum are avoided as the yield of molybdenum in the process according to the invention is almost l 00% Since the density of the composition causes it to sink to the slag/metal interface the loss of molybdenum that occurs by volatilisation of molybdic oxide briquettes is greatly diminished. Moreover the combination of porosityand density given by the compositions of the present invention facilitates their ready and rapid solution in the steel bath. In contrast, conventional ferromolybdenum is dense and tends to sink to the bottom of the steel bath and, as a result, gives a non-uniform distribution of the alloy in the steel bath.

The process of the invention is advantageous in being readily employable in a continuous manner. Moreover, since the product can be obtained in the form of small nodules of briquettes of predetermined weight, the addition of carefully controlled quantities of molybdenum to the steel is simplified.

The following examples illustrate the invention.

EXAMPLE 1 A mixture of 260 grams roasted molybdenite, 86 grams millscale (FeO) and 30 grams carbon was placed in a glass bottle of l kilogram capacity which was placed on revolving rollers for one hour to mix the contents. 15 grams molasses in 10 ml water was then added with stirring.

The wet mixture was formed into briquettes using a pressure of tons per squareinch. The briquettes were packed in carbon in a carbon crucible and introduced into an induction furnace. The purpose of the enveloping layer of carbon was to protect the briquettes from the oxidising atmosphere in the furnace. The temperature in the furnace was increased over a period of l /2 hours up to a temperature of 1320C. The temperature was maintained at this level for 2 hours and the crucible was then allowed to cool to room temperature.

The briquettes so formed each weighed about 67 grams, had a density of 2.8 grams per cubic centimeter and the following analysis, by weight:

molybdenum 64.6% iron .37: carbon 09%.

A chlorination test to indicate the slag content left a residue of 8.0%.

EXAMPLE 2 The procedure of Example I was followed. using a mixture of 290 grams roasted molybdenum, 75 grams millscale, 35 grams of charcoal and 15 grams of molasses. The temperature in the furnace was raised from ambient to l,33()C.

The briquettes so formed each weighed about 68 grams, had a density of 3.8 grams per cubic centimeter and, the following analysis, by weight:

molybdenum 69.4% iron 19.8% carbon L26) slag (chlorination test) We 'claim:

1. An additive for molten steel baths which consists lybdenum content is 60 to the iron content is 20 to 30% and the carbon content is 0.2 to 1.5%.

3. An additive as claimed in claim 1 wherein the density is within the range 3 to 4.

4. A method for making a porous, solid-shaped composition which permits ready dissolution at the interface between the molten steel and molten slag layer in a molten steel bath consisting essentially of and having by weight, a molybdenum content in the range 40 to an iron content in the range 10 to 50%, a carbon content in the range 0.2 to 5%, and a binder being a member of the group consisting of molasses, starch, dextrine and tar and a density in the range 2.5 to 5 grams per cubic centimeter which consists essentially of adding together a molybdenum-containing material, an iron-containing material, carbon and said binder and heating the mixture so formed at a temperature in the range 850 to 1500C. for a period of at least one hour. 1

5. A method as claimed in claim 4, wherein the molybdenum-containing material is molybdenum trioxide.

6. A method as claimed in claim 4, wherein the molybdenum-containing material is ammonium molybdate.

7. A method as claimed in claim 4, wherein the ironcontaining material is iron oxide.

8. A method as claimed in claim 4. wherein the ironcontaining material is ground iron.

9. A method as claimed in claim 4, wherein the iron containing material is of a particle size below 30 mesh BSS.

10. A method as claimed in claim 4, wherein the temperature is in the range 1 to l350C.

11. A method as claimed in claim 4. wherein the materials to form the composition are introduced into acold furnace which is then allowed to warm up to the desired temperature level.

12. An additive as claimed in claim 1 whcrein'the solidshapeis in the form of a briquette having a density of 2.8 and an analysis by weight of 64.6 molybdenum, 25.371 iron, 0.9% carbon and a slag content of 8.0%.

13. An additive as claimed in claim ,1 wherein the solid shape is in the form of a briquette having a density of 3.8 and an analysis by weight of 69.4% molybdenum, 19.8% iron, 1.2% carbon and a slag content of 8.8%. 

1. AN ADDITIVE FOR MOLTEN STEEL BATHS WHICH CONSISTS ESSENTIALLY OF A POROUS, SOLID-SHAPED COMPOSITION HAVING THE PROPERTY OF READY DISSOLUTION AT THE INTERFACE BETWEEN THE MOLTEN METAL AND MOLTEN SLAG LAVER AND HAVING BY WEIGHT, A MOLYBDENUM CONTENT IN THE RANGE 40 TO 95%, AN IRON CONTENT IN THE RANGE 10 TO 50%, A CARBON CONTENT IN THE RANGE 0.2 TO 5% AND AS A BINDER A NUMBER OF THE GROUP CONSISTING OF MOLASSES, STARCH, DEXTRINE AND TAR, THE DENSITY OF THE COMPOSITION BEING IN THE RANGE 2.5 TO 5 GRAMS PER CUBIC CENTIMETER.
 2. An additive as claimed in claim 1, wherein the molybdenum content is 60 to 70%, the iron content is 20 to 30% and the carbon content is 0.2 to 1.5%.
 3. An additive as claimed in claim 1 wherein the density is within the range 3 to
 4. 4. A method for making a porous, solid-shaped composition which permits ready dissolution at the interface between the molten steel and molten slag layer in a molten steel bath consisting essentially of and having by weight, a molybdenum content in the range 40 to 95%, an iron content in the range 10 to 50%, a carbon content in the range 0.2 to 5%, and a binder being a member of the group consisting of molasses, starch, dextrine and tar and a density in the range 2.5 to 5 grams per cubic centimeter which consists essentially of adding together a molybdenum-containing material, an iron-containing material, carbon and said binder and heating the mixture so formed at a temperature in the range 850* to 1500* C. for a period of at least one hour.
 5. A method as claimed in claim 4, wherein the molybdenum-containing material is molybdenum trioxide.
 6. A method as claimed in claim 4, wherein the molybdenum-containing material is ammonium molybdate.
 7. A method as claimed in claim 4, wherein the iron-containing material is iron oxide.
 8. A method as claimed in claim 4, wherein the iron-containing material is ground iron.
 9. A method as claimed in claim 4, wherein the iron-containing material is of a particle size below 30 mesh BSS.
 10. A method as claimed in claim 4, wherein the temperature is in the range 1150* to 1350*C.
 11. A method as claimed in claim 4, wherein the materials to form the composition are introduced into a cold furnace which is then allowed to warm up to the desired temperature level.
 12. An additive as claimed in claim 1 wherein the solid shape is in the form of a briquette having a density of 2.8 and an analysis by weight of 64.6 molybdenum, 25.3% iron, 0.9% carbon and a slag content of 8.0%.
 13. An additive as claimed in claim 1 wherein the solid shape is in the form of a briquette having a density of 3.8 and an analysis by weight of 69.4% molybdenum, 19.8% iron, 1.2% carbOn and a slag content of 8.8%. 